Inert gas shielded arc welding is known, and several prior patents teach apparatus for carrying out such welding. For example U.S. Pat. No. 4,599,505 (Lukens et al.) shows a gas shield with a skirted inert gas head. The head has an elongated trailing end and an electrode receiving port which is offset toward the leading edge of the head. The inert gas conduit within the head is perforated on the side away from the lens and releases the inert gas through the perforations. The head is packed with metal wool to aid diffusion of the inert gas. The head is generally hemicylindrical. The Luken et al. patent was issued on Jul. 8, 1986.
Other patents which may be pertinent are U.S. Pat. Nos. 3,521,023 (Dahlman); 4,300,034 (Schneider); 4,567,343 (Sullivan); and 4,625,095 (Das).
A problem in the art has been how to use inert gas shielded arc welding to build up the metal on a workpiece, such as a jet engine turbine rotor, along a circumferential work surface which lies under a parallel overhang of the workpiece and thus is only accessible from the side. Commercially available automated welding systems have their torch heads and inert gas skirts rigidly mounted in line with a conduit through which inert gas is introduced to the workpiece. Such a torch must be advanced to a work surface perpendicularly and receive inert gas through a supply conduit disposed perpendicularly with respect to the workpiece. The overhang of a turbine rotor will not permit such a torch to advance to the circumferential work surface in the proper alignment for welding.